In vertebrates, the immune system is responsible for the protection against pathogens
such as viruses, bacteria, fungi or parasites. This remarkably effective defense system
depends upon the white blood cells or leukocytes, which mediate both innate and
adaptive immune responses.
Innate immunity provides an immediate but non-specific front line of host
defense against many pathogens and involves granulocytes (neutrophils, eosinophils
and basophils), mast cells, macrophages and natural killer (NK) cells. Germ lineencoded
surface receptors to common pathogens constituents on innate effector cells
trigger the elimination of pathogens by phagocytosis and the release of inflammatory
mediators, such as cytokines and chemokines. These receptors are referred to as
pattern recognition receptors (PRRs), which recognize a limited set of molecules that
are broadly shared by pathogens but distinguishable from host molecules, collectively
referred to as pathogen-associated molecular patterns (PAMPs).
Acquired or adaptive immunity is characterized by gradual, though highly
specific and effective immune responses against pathogens. Three major cell types
are involved in adaptive immunity: B-lymphocytes, T-lymphocytes and antigen
presenting cells (APCs), the most potent of which are dendritic cells (DCs). DCs act as
messengers between the innate and adaptive immune system. Their main function is to
take up, process and present pathogen constituents (also called antigens) with major
histocompatibility complex (MHC) proteins to T lymphocytes. B- and T-lymphocytes are
considered to be the central players of the adaptive immune system. Their unique and
virtually limitless capacity to specifically recognize antigens relies on the generation of a
wide repertoire of antigen receptors – B-cell receptor (BCR) in B-lymphocytes and T-cell
receptor (TCR) in T-lymphocytes – during lymphocyte development. B-lymphocytes
respond to pathogens by producing large quantities of antibodies (secreted form of
BCR) with pathogen neutralizing capacities, when terminally differentiated into plasma
cells. In response to antigens, T-lymphocytes produce cytokines that direct the immune
response (T-helper cells) or toxic granules that induce the death of pathogen infected
cells (cytotoxic T-cells). Following pathogen elimination, lymphocytes leave a lasting
legacy of the antigens they have encountered in the form of memory cells, which are
able to mount faster and stronger immune responses in subsequent challenges with the
same antigen – a process know as immunological memory.
This thesis focuses on the role of specific transcription factors during lymphocyte
development and differentiation into functional effector subsets.http://repub.eur.nl/res/pub/21344/101117_Ribeiro%20de%20Almeida%2C%20Claudia%20Alexandra.pdf
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